Automate FTP Downloads

When I was a kid watching TV, nothing frustrated me more
than to see those terrible words… “To Be Continued.”
Good grief! You mean I have to wait a whole week to see
how it ends? You could tell when it was coming, too. The
clock read 7:52 and there were way too many loose ends
to tie up. I hated that. So you can imagine how much joy
it gave me to leave you hanging for an entire month. I’m
beginning to understand those television guys. What a
sense of power! Dogbert would be impressed.

Well, as the saying goes: “Good things come to those
who wait.” If you’ll recall, I promised to delve
deeper into the world of components by showing you how
to automate downloading files from an FTP site.

We’ll look at two ways of accomplishing this task:
the old way, using the DOS FTP utility, and a new way,
using the Windows Script Host (WSH) and a third-party
component from Mabry Software (www.mabry.com)
called FTPX. Either will accomplish the objective, but
I think you’ll find the latter provides more flexibility
and control.

The “Barney” Method (For Dinosaurs)

The DOS FTP utility is an interactive command-line tool
that allows you to connect to a site (either in ASCII
or binary mode) and perform any number of functions—uploading
or downloading a file, shelling to the OS, and so on.
You can write a script (.CMD or .BAT) to use this tool
by creating a text file with all of the appropriate commands
and using the “-s” flag, as shown below.

Each line from the text file is fed into the FTP utility
one line at a time. Once the end of the text file is reached,
control is handed back to the script.

Since this uses old-style batch scripts, there are several
limitations. For starters, you’re limited in the
amount of error-handling you can perform. Second, if you
need to change one or more of the parameters (such as
the FTP site, filename, or upload/download), you must
write another complete text file with all of the necessary
commands. This introduces many opportunities for mistakes,
even if you copy the original text file to a new file
and just change the required parameters. Other limitations
include the difficulties of connecting through a firewall
(one that requires logging in) or via a proxy server that
may or may not require you to connect via a different
port.

The 21st Century Method

Yeah, yeah… I know we don’t officially enter
the 21st century until January 1, 2001. Nevertheless,
it’s the year 2000 now; time put away the old ways
and embrace a new paradigm: Working Efficiently! (Heck
of a concept, no?) By using the WSH and a third-party
FTP component, we can gain unsurpassed power and efficiency
over automating this process. Let’s start by using
our old friend from last
month’s column, XRay.exe, to look at this component.

Figure 1 shows FTPX.DLL loaded into XRay. I’ve highlighted
the CONNECT method. I’ve chosen this particular method
because it demonstrates a capability we haven’t discussed
yet: optional parameters. Just as there are many different
ways to accomplish the same task in Windows, so it is
with components. Figure 1 lists LogonName, LogonPassword,
and Account as optional parameters. Since these parameters
correspond to properties of this object, we can set them
ahead of time if we so choose. The two scripts shown below
accomplish the same thing.

It’s up to you to decide which method you prefer.
(Hint: Once you’ve selected a method, you should
use it more or less exclusively!) My preference is to
preset as many parameters as I can. It may take a few
more lines of code, but it helps me to keep things organized.

Figure 1. Use the utility called
XRay.exe to view FTPX.DLL, which shows some optional
parameters.

Let’s Write Some Script

Now let’s write a script to connect to an ftp site,
download a file, save it to our local drive, and delete
it from the source. Of course, you’ll need to have
the appropriate privileges on the FTP site if you want
to delete files, as I do in the following example. This
script connects to an FTP site, downloads a file, saves
it locally, and deletes it from the source.

‘My FTP script
‘getandkill.vbs
‘Retrieves a file and deletes it from an FTP site

You’ll notice that in Section 2 I’ve “hardwired”
my filenames into the script. I could just as easily have
passed these parameters using the Wscript.Arguments component.
This would work for the LogonName and LogonPassword as
well. You can also see that I’ve set the Blocking
property to “True” (Section 3). This causes
the script to wait for successful completion of each command
before executing the next one. That’s very important
in this case, since I wouldn’t want to delete the
file before I was finished downloading it, now would I?
If I set this property to False, however, it allows me
to accomplish other tasks without waiting for previous
tasks to complete (try doing that with DOS FTP!). A “Done”
event will be fired as each task is completed. (We’ll
talk more about events and error handling in a future
column—soon, I promise.)

Now that we’ve got the file on our local drive,
we can use the Scripting Runtime FileSystemObject to copy
it, rename it, move it, or whatever we need to do to it.
Fortunately for us, though, this component is powerful
enough to take care of much of that work for us. We could
even preface the destination filename with the date or
some other identifier if we routinely downloaded files
of the same name. The possibilities are endless!

Next month we’ll round out our study of components
by looking at how we can accomplish common administrative
tasks using some very powerful objects that are built-in
to Windows. In other words… “To Be Continued!”